On Thu, Aug 01, 2019 at 12:28:13PM -0700, Frank Rowand wrote: > Hi Greg, > > On 7/31/19 11:12 PM, Greg Kroah-Hartman wrote: > > On Wed, Jul 31, 2019 at 03:17:13PM -0700, Saravana Kannan wrote: > >> Add device-links to track functional dependencies between devices > >> after they are created (but before they are probed) by looking at > >> their common DT bindings like clocks, interconnects, etc. > >> > >> Having functional dependencies automatically added before the devices > >> are probed, provides the following benefits: > >> > >> - Optimizes device probe order and avoids the useless work of > >> attempting probes of devices that will not probe successfully > >> (because their suppliers aren't present or haven't probed yet). > >> > >> For example, in a commonly available mobile SoC, registering just > >> one consumer device's driver at an initcall level earlier than the > >> supplier device's driver causes 11 failed probe attempts before the > >> consumer device probes successfully. This was with a kernel with all > >> the drivers statically compiled in. This problem gets a lot worse if > >> all the drivers are loaded as modules without direct symbol > >> dependencies. > >> > >> - Supplier devices like clock providers, interconnect providers, etc > >> need to keep the resources they provide active and at a particular > >> state(s) during boot up even if their current set of consumers don't > >> request the resource to be active. This is because the rest of the > >> consumers might not have probed yet and turning off the resource > >> before all the consumers have probed could lead to a hang or > >> undesired user experience. > >> > >> Some frameworks (Eg: regulator) handle this today by turning off > >> "unused" resources at late_initcall_sync and hoping all the devices > >> have probed by then. This is not a valid assumption for systems with > >> loadable modules. Other frameworks (Eg: clock) just don't handle > >> this due to the lack of a clear signal for when they can turn off > >> resources. This leads to downstream hacks to handle cases like this > >> that can easily be solved in the upstream kernel. > >> > >> By linking devices before they are probed, we give suppliers a clear > >> count of the number of dependent consumers. Once all of the > >> consumers are active, the suppliers can turn off the unused > >> resources without making assumptions about the number of consumers. > >> > >> By default we just add device-links to track "driver presence" (probe > >> succeeded) of the supplier device. If any other functionality provided > >> by device-links are needed, it is left to the consumer/supplier > >> devices to change the link when they probe. > > > > All now queued up in my driver-core-testing branch, and if 0-day is > > happy with this, will move it to my "real" driver-core-next branch in a > > day or so to get included in linux-next. > > I have been slow in getting my review out. > > This patch series is not yet ready for sending to Linus, so if putting > this in linux-next implies that it will be in your next pull request > to Linus, please do not put it in linux-next. It means that it will be in my pull request for 5.4-rc1, many many waeeks away from now. thanks, greg k-h
